acl_test.rb

require 'ffi'

class File
  class ACL
    extend FFI::Library
    ffi_lib :acl

    ACL_TYPE_ACCESS = 0x8000
    ACL_FIRST_ENTRY = 0
    ACL_NEXT_ENTRY  = 1

    ACL_USER_OBJ  = 0x01
    ACL_USER      = 0x02
    ACL_GROUP_OBJ = 0x04
    ACL_GROUP     = 0x08
    ACL_MASK      = 0x10
    ACL_OTHER     = 0x20

    attach_function :acl_get_file, [:string, :int], :pointer
    attach_function :acl_get_entry, [:pointer, :int, :pointer], :int
    attach_function :acl_get_tag_type, [:pointer, :pointer], :int
    attach_function :acl_free, [:pointer], :int
    attach_function :acl_to_text, [:pointer, :pointer], :string

    def initialize(file, access = ACL_TYPE_ACCESS)
      @acl = acl_get_file(file, access)

      if @acl.null?
        raise SystemCallError.new("acl_init", FFI.errno)
      end

      get_acl_info(@acl)

      ObjectSpace.define_finalizer(self, proc{ acl_free(@acl) })
    end

    def to_s
      len = FFI::MemoryPointer.new(:size_t)
      text = acl_to_text(@acl, len)

      if text.empty? || text.nil?
        raise SystemCallError.new("acl_to_text", FFI.errno)
      end

      text
    end

    def get_acl_info(acl)
      ent_ptr = FFI::MemoryPointer.new(:pointer)
      tag_ptr = FFI::MemoryPointer.new(:int)

      entry_id = ACL_FIRST_ENTRY

      while val = acl_get_entry(acl, entry_id, ent_ptr)
        break if val < 1

        # TODO: Fails. Why?
        if acl_get_tag_type(ent_ptr, tag_ptr) != 0
          raise SystemCallError.new("acl_get_tag_type", FFI.errno)
        end

        entry_id = ACL_NEXT_ENTRY
      end
    end

    private

    def tag_type(value)
      case value
        when ACL_USER_OBJ
          "user_obj"
        when ACL_USER
          "user"
        when ACL_GROUP_OBJ
          "group_obj"
        when ACL_GROUP
          "group"
        when ACL_MASK
          "mask"
        when ACL_OTHER
          "other"
        else
          "none"
      end
    end
  end
end

acl = File::ACL.new('test.txt')
#puts acl.to_s